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Curve Tracer Laboratory Assistant Using the Analog Discovery Module as A Curve Tracer
RIT Curve Tracer Lab Assistant Professor Bowman 1
The objective of this lab is to
become familiar with methods to
measure the dc current-voltage
(IV) behavior of diodes and
metal-oxide-semiconductor field-
effect transistors (MOSFETs).
In this exercise we will configure
the Analog Discovery module to
emulate a semiconductor curve
tracer. We will save these
instrument configurations as
Analog Discovery Workspace
files for use in future labs.
ALD 1103 NMOS Transfer Characteristics
What is A Curve Tracer?
RIT Curve Tracer Lab Assistant Professor Bowman 2
A curve tracer is an instrument that measures and plots the dc current-voltage
characteristics of a semiconductor device. For four terminal devices like MOSFETs, the
output (ID vs VDS) and transfer (ID vs VGS) characteristics are very useful in describing
device behavior. The plot below shows the output (ID vs VDS) behavior for a NMOSFET
device found in the ALD1103 IC array. This data was measured using the Analog
Discovery module configured as a curve tracer.
Output Characteristics
for ALD1103 NMOSFET
Y-Axis Scale is 10-2 A/V
VGS = 4V
VGS stepped in 0.5
V increments for 10
steps from 0 – 4V
IDS is determined
by measuring the
voltage across a
100 ohm resistor in
series with the drain
VD is swept from 0
to 5 V for each gate
step voltage VDS
IDS
Test Circuits for Characterizing
Semiconductor Devices
RIT Curve Tracer Lab Assistant Professor Bowman 3
The current-voltage (IV) behavior of diodes and metal-semiconductor field-effect transistors
(MOSFETs) is characterized by stimulating selected device terminals and measuring the
response. The IV response is measured using test set ups like those below. The value of
resistor R1 is scaled in size to develop about 4V across the resistor at maximum current for
the device under test. R1 = 10 Ω works well for the ALD1103 series NMOSFETs.
(a) Diode IV Curve (b) MOSFET Output IV Curve (c) MOSFET Transfer IV Curve
Some Observations about Configuring the
Analog Discovery Module as a Curve Tracer
RIT Curve Tracer Lab Assistant Professor Bowman 4
Diode characteristics like that in setup (a) are measured simply by sweeping VD
and measuring ID.
Configuring the Discovery module for MOSFET device measurement requires the
simultaneous stimulation of two separate device terminals as previously shown in
setups (b) and (c).
The differential scope channels of the Discovery module allow for convenient
measurement of differential voltages across elements like resistor R1. These
differential voltages convert directly to current by the resistor scale factor.
The terms sweep and step imply that device terminals are being changed over
time. As long as the stepping and sweeping is conducted at low frequencies the
measured characteristics will represent device dc behavior.
The measurement techniques will take advantage of the X-Y scope configuration
in the Waveform software for plotting either ID vs VDS or ID vs VGS for our test
setups. The X-Y scope mode defaults to Channel 2 Y-axis and Channel 1 X-axis.
Configuring the Discovery Module to
Measure NMOSFET Output Characteristics (ID vs VDS)
RIT Curve Tracer Lab Assistant Professor Bowman 5
The figure at the right is the test setup for
measuring NMOS output characteristics. The
drain voltage VD is swept over the desired range
by configuring AWG2 as a saw tooth waveform
generator. The gate voltage VGS is configured
as a staircase generator with the number of
steps and the incremental step size required.
AWG2 is set to run 10 X times as fast as AWG1
so that the drain current is swept for each gate
step value. As long as the time periods for the
AWG waveforms are on the order of
milliseconds MOSFET dc behavior is measured.
Scope channel probes are positioned to
measure ID (Ch2) and VDS (Ch1). Resistor R1
value is chosen to limit the voltage drop across
R1 to a maximum of 4V and to optimize the
current plot for the specific NMOSFET device.
RIT Curve Tracer Lab Assistant Professor Bowman 6
AWG Channel 1 Configured as a Gate Voltage Step Generator to
Measure NMOSFET Output Characteristics (ID vs VDS)
The Analog Discovery AWG 1 configured as a repetitive 10 step generator operating
a 100 Hz. With10 voltage steps of 0 to +4V the device exhibits increasing drain
current with increasing gate to to source voltage. Note the AWG 1 settings for the
VGS step generator below.
RIT Curve Tracer Lab Assistant Professor Bowman 7
AWG Channel 2 Configured as a Drain Voltage Sweep Generator
to Measure NMOSFET Output Characteristics (ID vs VDS)
The Analog Discovery AWG 2 is configured as a repetitive ramp generator operating at
1 KHz. This frequency is 10 times greater than the frequency of the gate voltage step
generator to complete a complete sweep for each gate step voltage. The voltage ramp
is between 0 and 5 V so that VDS forces the device drain current through all regions of
operation (cutoff, triode, saturation). Note the AWG2 settings for the ramp generator
below.
The ALD 1103 MOSFET IC (shown at the right)
contains 2 NMOS and 2 PMOS devices. You will
use 1 NMOS device in this test procedure.
These devices can be damaged if care is not
taken when connecting the pins! Also exercise
caution when handling MOSFETs. Your body
can generate thousands of volts of
electrostatic discharge.
Complete the test circuit setup (b) on your
solderless bread board including connections to
the Discovery module. Connect the ALD1103 DN1,
SN1, and V- (body) pins on the prototype board to
the appropriate locations in the test setup (b).
***As a special precaution connect the GN1
Gate pin last and remove GN1 first when wiring
devices on the bread board***
RIT Curve Tracer Lab Assistant Professor Bowman 8
The ALD1103 MOSFET Array Pin Diagram
RIT Curve Tracer Lab Assistant Professor Bowman 9
ALD1103 NMOSFET Output Characteristics (ID vs VDS)
VGS stepped in +0.5
V increments for 10
steps from 0 to +4V
IDS (10 mA/V)
VDS (V)
Download the Waveform workspace file NMOS Output Curve Tracer2 (ALD1103) into your
Discovery module. Now that you have carefully wired and verified the test circuit (b) on your
solderless breadboard, you can activate the Discovery module and measure the output
current-voltage (IV) behavior for the ALD1103 NMOSFET. Your results should resemble
that of the figure below.
Making the Output Trace Look Like a Curve Tracer
Converting the Y Axis to Units of Current
• To convert from volts to current we introduce
a custom math channel through the
Waveform software by right clicking on the
area of C1 and C2 to the right of the scope
trace and selecting Add Math Channel ->
Custom as shown at the right.
• Enter the function C2/10 to represent the
current as the voltage divided across R1
divided by the resistor (in this case 10 ohms).
• Set the Y axis units in the right pull down
menu to A for amperes.
• Right click in the XY#1 trace area and select
Channel 1 for X and Math 1 for Y.
• Adjust the math channel offset and range
values for an optimal display of current.
RIT Curve Tracer Lab Assistant Professor Bowman 10
RIT Curve Tracer Lab Assistant Professor Bowman 11
ALD1103 NMOSFET Output Characteristics (ID vs VDS)
Y Axis Scaled in Units of mA
Your results after inserting the custom math channel to set the Y axis to display current
should resemble that of the figure below.
VDS (V)
IDS (mA) VGS stepped in +0.5
V increments for 10
steps from 0 to +4V
Configuring the Discovery Module to Measure
NMOSFET Transfer Characteristics (ID vs VGS)
RIT Curve Tracer Lab Assistant Professor Bowman 12
The figure at the right is the test setup for
measuring NMOS transfer characteristics. The
drain voltage VD is fixed at +5V using the
Discovery V+ supply (don’t forget to power on).
The gate voltage VGS is swept over the desired
range by configuring the AWG2 as a saw tooth
waveform generator. AWG1 for VBS voltage is
configured as a staircase generator with the
number of steps and the incremental step size
required.
AWG2 is set to run 10 X times as fast as AWG1 so
that the drain current is swept for each body
terminal step value. As long as the time periods
for the AWG waveforms are on the order of
milliseconds MOSFET dc behavior is measured.
The scope channel probes are positioned to
measure ID (Ch2) and VGS (Ch1). R1 is chosen to
optimize the current plot for the NMOS device.
AWG Channel 1 Configured as a Body Voltage Step Generator to
Measure NMOSFET Transfer Characteristics
RIT Curve Tracer Lab Assistant Professor Bowman 13
The Analog Discovery AWG 1 configured as a repetitive 10 step generator operating
a 100 Hz. With10 voltage steps of 0 to - 4V the device exhibits increasing threshold
voltage with increasing negative body to source voltage. Note the AWG 1 settings for
the VBS step generator below.
AWG Channel 2 Configured as a Gate Voltage Sweep Generator to
Measure NMOS Transfer Characteristics
RIT Curve Tracer Lab Assistant Professor Bowman 14
The Analog Discovery AWG 2 is configured as a repetitive ramp generator operating at 1
KHz. This frequency is 10 times greater than the frequency of the body voltage step
generator to complete a complete gate voltage sweep for each body step voltage. The
gate voltage ramp is between 0 and 4 V so that VDS is always greater than VGS-VT to
keep the device in saturation. Note the AWG2 settings for the ramp generator below.
RIT Curve Tracer Lab Assistant Professor Bowman 15
Measuring ALD1103 NMOSFET Transfer Curves
with the Discovery Module
Download the Waveform workspace file NMOS Transfer Curve Tracer (ALD1103) V2
into your Discovery module. Now that you have carefully wired and verified the test
circuit (c) on your solderless breadboard, you can activate the Discovery module and
measure the output current-voltage (IV) behavior for the ALD1103 NMOSFET. Your
results should resemble that of the figure below.
VBS = 0 V
VBS = - 1 V
VBS = - 2 V
VBS = - 4 V
VBS = - 3 V
IDS (10 mA/V)
VGS (V)
RIT Curve Tracer Lab Assistant Professor Bowman 16
ALD1103 NMOSFET Transfer Characteristics (ID vs VGS)
Y Axis Scaled in Units of mA
IDS
VGS (V)
VBS = 0 V
VBS = - 1 V
VBS = - 2 V
VBS = - 4 V
VBS = - 3 V
Your results after inserting the custom math channel to set the Y axis
to display current should resemble that of the figure below.
RIT Curve Tracer Lab Assistant Professor Bowman 17
Measuring ALD1103 NMOSFET Transfer Curves
with the Discovery Module
PMOSFET Devices can be characterized much the same way using the Analog
Discovery module as a curve tracer. The test circuit configurations remain the same.
However, the PMOS device is complementary to the NMOS device and requires
reversing polarities on the terminal stimuli (AWGs and power supply). This conversion is
easily accomplished by starting with the NMOS Curve Tracer files.
For measuring PMOS output characteristics download the NMOS Output Curve
Tracer workspace file into the Analog Discovery module. Convert the gate voltage step
generator (AWG1) from positive polarity gate voltages to negative polarity gate voltages
by changing the amplitude from +2 V to – 2 V and the offset from + 2 V to – 2 V.
Likewise convert drain voltage sweep generator, AGW2, by changing the amplitude
from +2.5 to – 2.5 V and the offset from + 2.5V to – 2.5 V.
For measuring PMOS transfer characteristics download the NMOS Transfer Curve
Tracer workspace file into the Analog Discovery module. Convert the body voltage step
generator (AWG1) from negative polarity body voltages to polarity polarity gate voltages
by changing the amplitude from – 2 V to + 2 V and the offset from – 2 V to + 2 V.
Likewise convert the gate voltage sweep generator, AGW2, by changing the amplitude
from +2.5 to – 2.5 V and the offset from + 2.5V to – 2.5 V. Set VD to – 5V.
Once you have configured and verified the Discovery module for each test condition,
save each workspace file as PMOS Output Curve Tracer and PMOS Transfer Curve
Tracer. You will then have a library of standard MOSFET curve tracer configurations
RIT Curve Tracer Lab Assistant Professor Bowman 18
Measuring PMOS IV Curves with the Discovery Module
RIT Curve Tracer Lab Assistant Professor Bowman 19
ALD1103 PMOSFET Output Curves
Measured with the Discovery Module
IDS (100 mA/V)
VDS (V)
RIT Curve Tracer Lab Assistant Professor Bowman 20
ALD1103 PMOSFET Transfer Curves
Measured with the Discovery Module
VBS = 4 V
VBS = 3 V
VBS = 2 V
VBS = 0 V
VBS = 1 V
IDS (100 mA/V)
VDS (V)